I am setting up a system where a rectangular plate is heated by a set of heater cartridges, producing about 4000 watts. This plate is in free convection air. It is used to melt plastic at regular invervals. I am trying to model the system so we can estimate temperatures of the plate to control the system better, by using Simulink. I am having trouble linking several equations together though. I can figure out the temperature and time it takes to reach the temperature, in a vacuum at least, through Q=CM(Tf-Ti), and q=Q/t. The heaters are heated like a convection oven, electricity is either supplied or stopped, based on the temperature of the plate. What I am looking to do is find the temperature of the plate during a cycle, such as when temperature is roughly steady state, but is then decreased when energy is transfered to the plastic, and to air as well if I can. Does anyone have any idea how to calculate the temperature drop when it hits the plastic, and then how long it takes for the temperature to increase? I feel it is similar to say a fridge, it runs at a constant temperature until an item is put into it. The temperature drops and then rebounds. Thanks for any help that can be provided. Rich